Consumers prefer the natural flavor of fresh hand-squeezed citrus juice. Freshly extracted citrus juice is subjected to a concentration step to store and preserve the juice for year-round consumption. During concentration the sugar level is increased from about 10-15% to about 65%. At these high sugar levels, bacterial spoilage does not occur when the juice concentrate is preserved by cold storage. However, concentration processing techniques, such as evaporative concentration, can impair fresh flavor by removing desirable flavor and aroma volatiles and by creating undesirable thermal degradation flavors and aromas.
Evaporation removes water from fresh juice. The flavor and aroma compounds, which are primarily organic compounds, are removed with the vapor stream. The vapor stream condenses to a two-phase system. The water phase is referred to as "aqueous essence" and the oil phase is called "essence oil". Essence oil generally contains more of the higher molecular weight organics and typically is up to 95% limonene, whereas aqueous essence contains predominantly highly water soluble, low molecular weight alcohols (predominantly ethanol), aldehydes and esters. Adding these materials back to the concentrated juice improves its flavor, but the flavor often diminishes during storage.
The organic compounds believed to be primarily responsible for fresh valencia orange juice flavor are acetaldehyde, valencene, ethyl butyrate, neral and ethyl 3-hydroxyhexanoate. Compounds which are primarily found in citrus peel are generally considered detrimental to fresh flavor but, in small amounts, provide a citrus flavor. Degradation products such as decanal, alpha-terpineol, and d-carvone, and lipid oxidation products impart off-flavors to the juice.
It has now been found that fresh flavor compounds can be isolated from citrus extracts by a special dense gas extraction without concentrating the off-flavor materials. Liquid carbon dioxide has been used to isolate organic compounds from flavor-containing materials. For example, U.S. Pat. No. 3,477,856 to Schultz describes extracting materials such as fruit juices and fruit essences with liquid carbon dioxide, separating the extract, and evaporating the carbon dioxide. Pressures between about 900 psig and 1000 psig and temperatures less than 31.degree. C. (87.degree. F.) are preferred. Schultz discloses that liquid carbon dioxide can totally dissolve esters, alcohols, ketones, and aldehydes up to a molecular weight of 150.
Schultz and Randall, "Liquid Carbon Dioxide for Selective Aroma Extraction", Food Technology, 24, 1281-86 (1970), discloses that liquid carbon dioxide is a selective solvent for the aroma constituents of fruits. Concentrated aroma constituents were extracted from orange juice with a single-stage apparatus at room temperature and 918 psig.
In Schultz et al., "Pilot Plant Extraction with Liquid CO.sub.2,", Food Technology, 28 No. 6, 32-36, 88 (1974), liquid carbon dioxide was found to be a solvent for esters, alcohols, aldehydes, and ketones, which are typically found in fruit essences. Extractability of a compound in liquid carbon dioxide was said to depend on its structure, molecular weight, and partition coefficient between water and liquid carbon dioxide.
Carbon dioxide in the supercritical state has also been used for related extractions. For example, Gerard, "Continuous Terpene Removal from Essential Oils by Countercurrent Extraction with Compressed Carbondioxide", Chem.-Ing.-Tech. 56 No. 10, 794-95 (1984), discloses the selective extraction of pineapple essential oils by supercritical carbon dioxide. Limonene was fractionated from carvone with carbon dioxide at a pressure of 1200 psi and a temperature between 70.degree. C. (158.degree. F.) and 100.degree. C. (212.degree. F.) In a model mixture, caryophyllen was said to be separable from anethole at pressures between 1280 psi and 1350 psi and a temperature of 40.degree. C. (104.degree. F.).
At a meeting of the American Institute of Chemical Engineers (Nov. 27, 1984), it was reported that Robey used supercritical carbon dioxide at 60.degree. C. and 1600 psi to extract all the volatile components from lemon peel oil (95% limonene). Then the temperature was dropped at a constant pressure of 1600 psi to produce a mixture enriched in citral.
Lastly, in Brogle, "CO.sub.2 as a Solvent: Its Properties and Applications", Chemistry and Industry, June 19, 1982, pp. 385-90, it is stated that given a range of compounds with comparable polarity, the volatility and solubility in a given solvent decrease with rising molecular weight. A model natural product was extracted with carbon dioxide until all material was dissolved. The first compounds extracted were the very volatile compounds, such as the components of essential oils, then compounds such as the heavier terpenes followed by the fatty oils, and finally waxes, resins, and pigments.
Gerard and Robey use supercritical carbon dioxide to separate limonene from carvone, caryophyllone from anethole, and citral from limonene. These compounds all have a molecular weight greater than that of limonene. By contrast, most of the desirable organic citrus flavor and aroma compounds which contribute to fresh-tasting juice have molecular weights less than that of limonene.
It is an object of this invention to produce desirable citrus flavor and aroma compositions by purifying or rectifying the mixture of citrus organic flavor and aroma compounds so that most of the off-flavor contributors are removed and most of the positive fresh citrus flavor and aroma contributing compounds are remaining.
It is another object of this invention to conduct the rectification and collection of positive citrus flavor and aroma compounds by capturing the very low molecular weight, volatile materials in a high molecular weight mixture that is predominantly limonene and valencene. This mixture is further characterized in that it contains few or none of the off-flavor compounds, e.g. linalool, decanol, alpha-terpineol and nootkatone.
It is a further object of this invention to rectify the organic citrus flavor and aroma compounds by extraction with a dense solvent gas.
It is another object of this invention to produce citrus juice and citrus beverages having a taste like fresh-squeezed juice by adding the extracted citrus flavor and aroma compositions to a concentrated juice.
These and other objects of the invention will become evident from the disclosure herein.
All percentages are by weight unless otherwise defined.